1. Field of the Invention
The present invention relates to a digital comparator.
2. Description of Related Art
A comparator is known as a measuring instrument that measures a dimensional difference of a workpiece relative to a master workpiece. For example, a comparator disclosed in Japanese Unexamined Patent Application Publication No. 2002-131004 includes a frame, a spindle and an anvil, which are provided on the frame, biasing means, separation means, an indicator, and indicator driving means.
The spindle and the anvil are supported by the frame so as to be advanceable and retractable in the axial direction thereof to move toward and away from each other. The biasing means is provided on the frame and biases the anvil toward the spindle. The separation means retracts the anvil relative to the spindle against the biasing means. The indicator driving means is provided on the frame and transmits the movement of the anvil to the indicator.
In order to measure a dimensional difference of a workpiece relative to a master workpiece in the structure described above, the anvil is first retracted away from the spindle by the separation means. Then, after the master workpiece is inserted between the anvil and the spindle, the separation operation of the separation means is released to advance the anvil toward the spindle by the biasing means.
As a result, the master workpiece is held between the anvil and the spindle. At this time, the spindle is moved in the axial direction thereof, or the dial of the indicator is rotated, to thereby conduct zero adjustment of a pointer. Subsequently, after the anvil is retracted by the separation means to detach the master workpiece from the comparator, a workpiece is held and measured between the anvil and the spindle in the same operation. Accordingly, the value of the indicator can be measured as a dimensional difference of the workpiece relative to the master workpiece.